Means to expand sensitivity of spectral wave length region of silver halide emulsion, to enhance sensitivity is well-known as spectral sensitization. As for spectral sensitizing dye used for this purpose, a lot of compounds such as cyanine dyes and merocyanine dyes are known.
These spectral sensitization dyes are required not only to be capable of expanding light-sensitive wave length region of silver halide emulsion, but also to satisfy various other conditions given below:
1) The spectral sensitizing region is appropriate. PA1 2) The spectral sensitization efficiency is high. PA1 3) Occurrence of fog, gamma change, etc. do not adversely affect the characteristic curve. PA1 4) When the silver halide photographic light-sensitive material comprising the sensitizing dye, especially when it is preserved for a long period of time under conditions of high humidity and high temperature), photographic properties such as fog do not change. PA1 5) The dye incorporated does not diffuse to another layer of different spectral sensitivity and 6) the dye does not cause color contamination. PA1 6) Color staining does not cause after development, fixation and washing or stabilization processes are completed due to dissolving of the dye into processing solution. However, the sensitizing dyes heretofore known in the art do not fully satisfy all these conditions, And they have not come up to the standard.
Especially, since processing time of the photographic material has become shorter and processing without washing or rinsing step with recycling use of the processing solution is adopted, the dye becomes more liable to remain in the photographic material. As a result, color contamination, which is hereinafter called as color stain, comes to take place easily in the photographic material and this remarkably damages the product value of the photographic material. In other words, as far as the sensitizing dyes are concerned, improvement in anti- color-staining property has become an important technical problem to be solved.
As the sensitizing dye which is capable of increasing sensitivity in red light wave length region, validity of the following dyes are known in the art. They are, for example, complex cyanine dyes and complex merocyanine dyes disclosed in Belgian Patent No. 541,245; U.S. Pat. Nos. 2,493,747, 2,743,272 and 3,335,010; French Patent No. 2,113,248; German Patents No. 1,024,800, 2,153,570 and 2,300,321; and Japanese Patent O.P.I. Publication Nos. 171135(1991); cyanine dyes disclosed in Japanese Patent O.P.I. Publications Nos. 11121(1974), 33622(1976), 115821(1976), and 115822(1976), 72937(1983), 203446(1986), Japanese Patent O.P.I. Publications Nos. 256045 (1991) and 1504251 (1991); Merocyanine dyes disclosed in Japanese Patent O.P.I. Publications Nos. 106422(1976) and 214030(1984); U.S. Pat. Nos. 2,493,747, 2,493,748 and 2,519,001. Cyanine dyes disclosed in Japanese Patent O.P.I. Publications Nos. 11121(1974), 33622(1976), 115821(1976) issues, and 115822(1976), 72937(1983), 203446(1986), Japanese Patent O.P.I. Publications Nos. 256045(1990), and 1504251(1991). It is a merocyanine dye of the description in each official report such as each specification, Japanese Patent O.P.I. Publication Nos. 106422(1970) issues, and 214030(1984) issues such as U.S. Pat. No. 2,493,747 issues, 2,493,748 issues, and 2,519,001 issues. The validity of these dyes is known. As for a part of these dyes, the color stain due to remaining dye may be reduced by introducing a water-solubilizing group in the molecule. However, it is not sufficient and has the problem such as causing the sensitivity variation depending on the aging of falling off of the spectral sensitization sensitivity and coating solution easily by storing the coating solution. The performance of these dyes are not still unsatisfactory.
In recent years, those dyes disclosed in European Patents No. 363,104 and 363,107 have a remarkable improved effect in anti-color-staining property. However, there is a problem that the photographic properties of the photographic material which has been optically sensitized by the use of these dyes tends to change easily with the lapse of time.
Moreover, in Japanese Patent O.P.I. Publications No. 54-18726(1979), 59-135461(1984), and 62-246045(1987) disclose a technique, by which spectral sensitivity is enhanced by using a sensitizing dye together with a certain kind of supersensitizing agent and the load of color staining is reduced, is disclosed. However, the effect of this technique still remains at an insufficient level and the further improvement is requested.